This invention relates generally to apparatus and methodology useful in effecting medical diagnosis, and more specifically, relates to systems and methodology utilizing ultrasonic techniques for such purposes.
Over the course of the last several decades, ultrasonic technology has played an ever-increasing role in medical diagnostics. Such techniques find application in diagnosis of various medical ailments wherein it is useful to examine internal bodily organs, with the objective of locating features or aspects of such organs which may be indicative of disease, abnormalities or so forth.
While early systems of the foregoing type included but limited capabilities and display functions, there have more recently come into use highly sophisticated devices which are capable of providing real time or recorded displays with excellent detail and good resolution of desired portions of the body being considered.
In a typical such device, and one to which the present invention is directly applicable, the transducer means and imaging system provides a cross-sectional image of an internal body portion with the transducer elements being scanned to interrogate the corresponding linear section of the body portion. Such scanning may be effected mechanically by oscillating transducer elements through said angular sector or rotating transducer elements to effect a similar result or electronically, by means of a linear array or a phased array wherein the elements, although stationary, are electronically actuated so as to produce a sound beam which scans through the interrogated cross-sectional area. In such a linear array system, a plurality of transducer elements are arranged in a side by side fashion to extend over a length of perhaps 10 to 15 centimeters. As each transducer element is activated it sends a sound beam directly into the contacting body. Any acoustical impedance variations within the body will cause some of the sound beam to be reflected back toward the transducer. The same transducer element will interrupt the returning sound energy and convert it back to electrical energy. This electrical signal is then processed and may be displayed upon a CRT screen as one line of image data. Next, the adjacent transducer element is pulsed and any reflected signals from it are displayed as an adjacent line of image data on the CRT screen. This process is repeated for each of the remaining transducer elements as a two-dimensional image is built up on the CRT screen. The final image will contain a number of parallel lines of data representing a rectangular cross-section of acoustical impedance variations within the body being examined.
In the phased array a plurality of transducer elements is arranged in compact linear fashion. Each transducer element is individually connected to a suitable transmitter and receiver, and the transmitted pulses are so phased as to steer the emitted sound beam in the desired direction. Adjustable delays provided in each receiver channel enhance the reception from the same direction as the transmitted sound beam. By suitably controlling the time of the voltages applied to the transducer elements and by controlling the adjustable delays of the separate receiver channels, the beam can be steered to any desired angle of a fan-shaped sector.
Operation of the phased array is such that a plurality of radial lines defining the fan-shaped sector are successively generated, with a relatively high number of such radial lines--typically of the order of 128 such lines--being utilized in the course of generating the entire sector. The set of such lines is generated over a short period, typically of the order of 1/30th of a second, whereby the corresponding display on the system cathode ray tube (CRT) is a high resolution, substantially real time image of the bodily portion being examined. This visualization is, in the terminology of the present art, a so-called B-mode display, i.e., one wherein variations of the acoustical impedance of the tissues are translated into brightness variations on the CRT screen.
Details regarding the prior art signal processing techniques utilized in apparatus of the foregoing type in order to generate the mentioned fan-shaped sector image are set forth in a number of points in the prior art. Reference may usefully be had, for example, to U.S. Pat. No. 4,005,382 to William Beaver, entitled "Signal Processor for Ultrasonic Imaging", which patent is assigned to the assignee of the present application.
It may further be noted that apparatus of the type to which the present invention is applicable, which apparatus is in substantial accord with the foregoing description, is available commercially from the assignee of the instant application, Varian Associates, Inc. of Palo Alto, Calif., under Model No. V-3000, which is further described as a "Phased Array Ultrasonograph".
In apparatus of the foregoing type, the linear array of transducer elements is normally carried by a transducer body, which is a hand-held or hand-manipulated probe, the longitudinal axis of which is approximately aligned with the plane of the fan-shaped ultrasonic beam, which axis therefore approximately symmetrically divides the included angle of the fan.
In a typical mode of utilization, the physician or technician performing the diagnosis places the forward sound beam-emitting end of the transducer body in contact with the body of the patient, and angulates the transducer body so as to orient its longitudinal axis at an appropriate position to obtain imaging of a desired portion of bodily tissue being examined. It will be appreciated in this connection that the fan-shaped ultrasonic beam is present in what is substantially a plane, and thus one normally examines a two-dimensional image (as for example, on the mentioned CRT screen) of the bodily tissue intersected by the said fan-shaped beam.
It will further be appreciated, that in many instances the physician or technician is not satisfied to examine cross-sections alone; his interest may reside in determining the shape or especially the volume of certain bodily organs or voids. For example, in a number of instances concerned with cardiac studies, it is highly desirable to know the volume of a heart chamber, as for example, of the left ventricle. In other types of situations, for example, in certain conditions of pregnancy, it is highly desirable to be apprised of the fetal volume.
Prior methodology using ultrasonic imaging apparatus of the foregoing type has not, however, been adequate to enable the desired volume measurements or shape determinations. Thus, it will be evident that where the transducer body is merely freely manipulated by hand, there is no known determinative relation between transducer body angularity and the resulting image; and under such circumstances the examining physician or technician can at most, effect highly qualitative evaluations, i.e, essentially such evaluator is compelled to observe the imaging screen while simultaneously changing the angle of the transducer body, without, however, having any exact information on the actual angularity.
While in some instances, apparatus of the foregoing type has been equipped with complex positioning arms for the transducer body, which enable rather precise manipulation of same, these highly bulky arrangements have different objectives than measuring volumes. In particular they are merely intended to orient the transducer body axis to enable one specific two-dimensional view. Furthermore, such arms interfere with ease of transducer manipulation by the physician or technician.
In accordance with the foregoing, it may be regarded as an object of the present invention to provide an improvement system in evaluating the volume or shape of a three-dimensional for an ultrasonic imaging system, which enables use of the said portion of the bodily tissue being examined.